1. Fields of the Invention
This present invention relates to a method of synthesizing copper selenide powder and more particularly, to a method, which employs a very weak chelating agent to chelate copper and selenium ions and which comprises injecting a copper ion solution instantly into a selenium solution to form a mixed solution at a certain temperature and adding quickly a proper amount of reducing agent into the mixed solution for obtaining copper selenide powder.
2. Descriptions of Related Art
Copper selenide is one of the most important materials for p-type semiconductors and has been applied widely in industry for making solar cell, gas sensor, super ionic conductor and thermoelectric converter.
Copper selenide, however, exists in a stoichiometric form, such as CuSe), CuSe, Cu2Se, Cu3Se2, or in a non-stoichiometric form, such as Cu2-xSe.
Yet, literatures and documents have not revealed that the synthesis of Cu2-xSe and CuSe powder can be achieved merely by adjusting the dosage of one reducing agent.
By using hot-injection method, copper chloride is dissolved in TEG (triethylene glycol) in order to achieve cationic precursor and selenium powder is mixed with TEG and PVP (polyvinylpyrrolidone) in order to obtain anionic precursor. Then the cationic precursor is instantly injected into the anionic precursor solution and then adding 0.005 ml of TETA (triethylenetetramine) under a temperature of 210° C. Thereafter, the temperature of the solution would be maintained at 210° C. for 45 minutes and then cooled to 80° C. The Pyrite-CuSe2 powder can be produced after being repeatedly centrifuged and washed by ethanol. (T. Liu, Z. Jin, J. Li, J. Wang, D. Wang, J. Lai and H. Du, “Monodispersed octahedral-shaped pyrite CuSe2 particles by polyol solution chemical synthesis,” CrystEngComm 15 (2013), 8903-8906)
In ion exchange process, selenium powder is mixed thoroughly with deionized water, 1M of sodium hydroxymethanesulfinate and 2M of ammonium hydroxide until the solution is clear in order to obtain an anionic precursor. Then, the anionic precursor is added into 0.3M of copper nitrate solution as a cationic precursor and stirred at 25° C. until the solution being black and some precipitates having appeared. The precipitates are then centrifuged with ultra pure water repeatedly to obtain CuSe. (O. Arellano-Tánori, M. C. Acosta-Enriquez, R. Ochoa-Landin, R. Iñiguez-Palomares, T. Mendivil-Reynoso, M. Flores-Acosta, S. J. Castillo, “Copper-Selenide And Copper-Telluride Composites Powders Sintetized By Ionic Exchange” Chalcogenide Letters (2014), 13-19.)
Alternatively, cationic precursor can be obtained by mixing copper chloride and ethylenediamine at room temperature for 10 minutes. Anionic precursor can be obtained by mixing selenium powder and hydrazine at room temperature for 10 minutes. Then, the cationic precursor is injected into the anionic precursor solution instantly. The mixed solution is stirred at room temperature until the brown precipitates having appeared. Then, the precipitates are centrifuged with ultra pure water to obtain Cu, Se powder. (P. Hu, Y. Cao, Synthesis of rod and lath-shaped CuSe and tremella-shaped Cu2-xSe nanostructures at room temperature, and their optical properties” J Nanopart Res (2012) 1-8)
In view of the foregoing, it is known that the synthesis of CuSe or Cu2-xSe powder could be done by using various chelating agents under different reaction conditions, sometimes even using toxic chemicals such as hydrazine, which is dangerous and may be harmful to the environment.